In lieu of prevention and early diagnosis, optimal treatment strategies are the most important variable in effective control of breast cancer. We hypothesize that patterns of gene expression exist that will distinguish primary breast cancers that are sensitive or resistant to specific chemotherapies. This project will establish gene expression parameters of response for two mainline chemotherapies for breast cancer: Taxotere (T), and Adriamycin (doxorubiein) plus cyclophosphamide (AC). We will use cDNA microarrays and allied technologies, e.g. QRT-PCR or immunohistochemistry (IHC), to identify and confirm patterns of gene expression associated with sensitivity or resistance to these two therapies. Our preliminary data strongly suggests that differential gene expression correlates with T response. Sensitive tumors have higher RNA expression of mitochrondrial proteins, inflammatory-response proteins, and motility-related microfilament proteins. Resistant tumors show elevated levels of beta tubulin, increased proliferation (KI67), and elevated oncogene expression levels. We will extend these preliminary expression array results by analyzing additional specimens, both sensitive and resistant tumors, and confirm key expression differences by IHC and QRT-PCR. As this profile differs from the expected profile of general chemoresistance, we hypothesize that this molecular portrait is specific for T sensitivity and resistance. From frozen core biopsies taken from the primary tumors before treatment, we will next prospectively validate in a randomizcd clinical trial the expression profile for T sensitivity and identify a parallel expression profile for AC chemotherapy sensitivity. From these expression array results, genes whose expression could distinguish between T and AC sensitivity may be identified. We then plan to develop a panel of specific predictive markers for T and AC, and validate their effectiveness in predicting responses on paraffin-embedded archival tissue from patients treated with either regimen. We will validate 5-10 of the most relevant and specific markers for each regimen. This project will identify, confirm, and validate prospectively and retrospectively, key genetic pathways involved in the sensitivity and resistance of the two main treatment regimens in breast cancer, T and AC. Identification of these pathways may lead to optimization of treatment for individual patients, and thereby reduce over-treatment, unnecessary toxicity, and overall cost.